1. Field of the Invention
The present invention relates to an output torque calculating apparatus and an output torque calculating method, and more particularly to a technique of calculating output torque with dead time in a driving source being removed.
2. Description of the Background Art
Automatic transmissions for automatically shifting gears are conventionally known. An automatic transmission forms, for example, a gear corresponding to a combination of engaged friction engagement elements among a plurality of friction engagement elements. The engaging force of the friction engagement elements is determined according to hydraulic pressure supplied to the friction engagement elements. In other words, the automatic transmission is hydraulically operated. The hydraulic pressure is generated, for example, by an oil pump driven by an engine.
In order to improve fuel efficiency, it is desired to reduce load on the oil pump as much as possible. In order to reduce load on the oil pump, the hydraulic pressure supplied to the friction engagement elements is reduced. However, if the hydraulic pressure supplied to the friction engagement elements is too low, the friction engagement elements may slip. Therefore, it is desired to realize such hydraulic pressure that is neither too low nor too high for output torque of the engine by exactly grasping input torque of the automatic transmission, that is, output torque of the engine.
Japanese Patent Laying-Open No. 2006-46177 discloses an engine torque calculating method including the steps of: calculating first engine torque based on an engine speed and an ignition timing of each cylinder; and calculating second engine torque used to control an automatic transmission by smoothing the first engine torque, based on a variation amount of the ignition timing of each cylinder.
According to the torque calculating method disclosed in Japanese Patent Laying-Open No. 2006-46177, the first engine torque (actual engine indicated torque) is calculated based on an engine speed. The second engine torque (actual engine net torque) is calculated, for example, by a smoothing process of repeatedly calculating the actual engine indicated torque and adding an addition value calculated based on a difference between the actual engine indicated torque calculated last time and the actual engine indicated torque calculated this time, to the actual engine indicated torque calculated last time. When the variation amount of the ignition timing is large, the addition value is reduced as compared with when it is small. Accordingly, even when the variation amount of the actual engine indicated torque is large, it is possible to calculate the actual engine net torque that varies smoothly, because of the smoothing process. Therefore, a rapid change of the actual engine net torque can be prevented. As a result, it is possible to calculate the torque that is preferred in controlling the automatic transmission.
Here, a certain time is required to adjust hydraulic pressure for use in control of the automatic transmission, to the desired hydraulic pressure. Therefore, the exact hydraulic pressure is not always obtained for the output torque obtained based on an operation state of the engine. If the output torque changes during adjustment of hydraulic pressure, even when the hydraulic pressure reaches a target value, that hydraulic pressure may be too high or too low for the output torque at that time. Thus, in order to accurately match the output torque of the engine with the hydraulic pressure for use in control of the automatic transmission, it is desirable to grasp the future output torque in advance and adjust beforehand the hydraulic pressure so as not to be too high or too low for the future output torque. However, the actual engine net torque calculated by the torque calculating method disclosed in Japanese Patent Laying-Open No. 2006-46177 is the output toque based on the operation state of the engine during the actual time and is not the future output torque.